Endless processing of a belt by vulcanization bonding is widely known.
Typical endless processing is as follows. First, a part of surface rubber 204 at both longitudinal ends 200a and 200b of a belt is cut and removed, and then core body canvas at both ends 200a and 200b is peeled off stepwise to form steps, as illustrated in FIG. 2A. Next, an adhesion processing material 202 such as rubber cement and unvulcanized adhesive rubber is attached to step surfaces 201, and the ends 200a and 200b are overlapped so that a depression 203 is formed between the belt longitudinal ends of the surface rubber of the belt, as illustrated in FIG. 2B. After this, the depression 203 to which the adhesion processing material 202 is attached is coated with at least one layer of unvulcanized rubber sheet, e.g. two layers of unvulcanized rubber sheets 210a and 210b, and the upper surface of the upper unvulcanized rubber sheet 210b is pressed with a roller 300 to pressure-join the unvulcanized rubber sheets 210a and 210b, the adhesion processing material 202, and the surface rubber 204 including the depression 203, as illustrated in FIG. 2C. The overlapped belt longitudinal ends including the depression 203 are then heated while being pressed from above and below, as a result of which the unvulcanized rubber sheets 210a and 210b are vulcanized to bond to the adjacent rubber. The endless belt can be manufactured in this way.
Here, the attachability between the adhesion processing material 202 and the vulcanized surface rubber 204 of the belt is typically not high. There is accordingly a possibility that, even when the upper surface of the upper unvulcanized rubber sheet 210b is pressed with the roller 300 as illustrated in FIG. 2C, the unvulcanized rubber sheets 210a and 210b and the adhesion processing material 202 peel away from the surface rubber 204 before vulcanization and as a result the work efficiency of the vulcanization step decreases significantly or the contamination with foreign substances occurs.
The following operation may also be performed after the depression 203 is coated with the unvulcanized rubber sheets 210a and 210b. The part of the unvulcanized rubber sheets 210a and 210b disposed on the surface rubber 204 is cut and removed so that the surface of the unvulcanized rubber sheets 210a and 210b is substantially level with the surface of the surface rubber 204, and then the unvulcanized rubber sheets 210a and 210b are vulcanized, as illustrated in FIG. 3A. Further, to improve the external appearance, both belt longitudinal ends of the vulcanized rubber sheets are buffed to make the edges 203e of the depression visible, as illustrated in FIG. 3B. In such a case, however, there is a possibility that the adhesion processing material 202 degrades as a result of being exposed at the edges 203e of the depression, causing the belt to be cracked at the edges 203e, and the vulcanized rubber sheets 210a and 210b to completely peel away from the exposed part of the interface of the vulcanized rubber sheets indicated by the arrows in the drawing.
It could therefore be helpful to provide a method for manufacturing an endless belt by which the work efficiency of endless processing can be enhanced and a highly durable endless belt can be obtained, and a highly durable endless belt.